Can you use two computers to render in Cycles?
If you are rendering a single image

(Alternative solution)

Since you are using Cycles, you can render the same scene on the two computers using half the number of Render samples on each one, then compositing them (in GIMP or in Blender), superimposing one onto the other with 50% opacity.

The two computers must use two different values (like, 0 and 1) for "Seed", otherwise you'll only get the same exact image, with half the shading quality, twice.



Grant Davis in a comment suggests that each instance of blender should output an OpenEXR image, which allows for a finer memory representation of color, so that less information is lost on the way to the final image.

Once the two computers have created their renders and saved as .exr, open a new blender instance and set the render size to the same it was in your scene. Then create your compositing nodes: two image inputs and a mix node.

Here, each image was rendered with full global illumination at 128 samples. You can see the top one when I mute (M) the Mix node. The mixed version has a quality comparable to a 256 samples render.





For animations, Tooniis' solution works fine.